accessing the social graph

This is important because it allows services to do the "Facebook" thing, without requiring users to have their whole lives in Facebook. It breaks out of the barriers of a particular service (although it still relies upon the all-powerful Google) and lets services build across multiple foundations. It definitely provides a better bet in the long run (because who knows how long the Facebook thing will last), and there's a lot that FB doesn't necessarily have access to. It won't be as neat and pre-packaged as the Facebook tools can be, but it will probably provide better results and a lot more value in the long run. TechCrunch has an article that gives much better details.